Grant,
You might give Egge Machine a call. I think they can make just about any size and type piston you would want. When I called about a set of pistons for a GMC 302 they said a custom set would cost around $350. I didn't think that was too bad for a custom job, considering a new set of Venolias were $500. Their web site: http://www.egge.com/

Here is another list of piston manufactures. Some will be able to make custom sets also. http://www.flatlanderracing.com/pistons.html

"The Operation of GMC trucks is normally smooth and steady, with no loud rattling, knocking or unusual noises. A good driver will quickly become accustomed to driving a GMC truck and will get the feel of his vehicle regardless of his engineering knowledge."-TM10-1563